Alternating current relay



Dec. 21,1943. J KNUDSEN 7 2,337,251

ALTERNATING CURRENT RELAY Filed Sept. 22, 1939 y mar m:

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Rf/ERS/BL mo-r 0 T'O PIE! INVENTOR. KNUD \J. KNUDSEN HIS ATTORNEY.

Patented Dec. 21, 1943 ALTERNATING CURRENT RELAY Knud J. Knudsen, Cleveland, Ohio, assignor to The Hickok Electrical Instrument Company, Cleveland, Ohio, a corporation of Ohio Application September 22, 1939, Serial No. 296,128

9 Claims.

This invention relates to relays and relay cir cuits and more particularly to an alternating current polarized tuned relay of extremely high sensitivity and the combination thereof with a control circuit.

For purposes of illustration the invention is described herein particularly as a radio control homing device for airplanes, but is not to be limited thereto, its use in connection with other steering devices, triangulation devices and the like being readily apparent from the exemplary description.

Polarized alternating current relays of the prior art are not suitable for use under conditions requiring both h gh sensitivity and snap action for the relay contacts because of inherent limitations in their operating characteristics. As one example, the armatures of prior relays are magnetically centered by the field and a relatively large portion of the armature current is rendered useless for applying pressure to the contacts because it is used in merely overcoming the centering effect of the field. The armature, in efiect, is held in a condition of relatively stable equilibrium magnetically.

To provide a snap action, it is necessary that the armature physically contact the polarizing pole faces, or at least approach very closely thereto. In the prior relays, contact between the armature and pole faces for obtaining the desired snap action, would make it necessary either to reduce the magnetizing current for the pole pieces or greatly increase the current in the armature to free the armature from the poles, or restore it to the neutral position.

However, most applications of such relays require a relay such that the armature at all times is free to move quickly to one or the other of the operated positions to or through the neutral position without the necessity of field current diminution or large increases in armature currents.

Furthermore, prior polarized alternating current rela s have been operable ace rately only by alternating cu rents having a sinusoidal wave shape, yet for many applications it is desirable that the relays be responsive to alternating currents having non-sinusoidal wave shapes such as alternating currents containing a great many harmonics. This is particularly true in connection with homing compasses and control circuits wherein the available operating current for the relay usually is the output from an electronic oscillator circuit.

An object of this invention is to provide an alternating current polarized relay which has extremely high sensitivity; which operates on veri low amperage currents and low watt input; which operates with a snap action for making and reaking contact; which is substantially free from flutter and the eiiects oi harmonics in the circuit; and which, therefore, responds accurately to alternating currents having a non-sinusoidal wave shape as well as to alternating currents hav ng a sinusoidal wave shape.

Another object is to provide a new combination of the relay and a control circuit for the automatic steering of air craft or other moving vehicles by radio control or for the determination of directions from any location to a sending station.

Another object is the combination of a high sensitivity relay with sensitive snap-acting switches which may form an operating part thereof, so as to provide accurate operation and eiiicient contact for controlling operations of mechanisms to be controlled electrically.

A more specific object is to provide a relay of the general character described in which the effect of harmonics is eliminated or reduced by shading the pole in a manner rendered effective by the cooperative relation of the armature and pole and in which the armature contacts the pole in a manner such that only one half of the magnetic field materially affects the armature for holding it in contact with the pole.

Another object is to provide a relay for use with a radio receiver having a loop which is rotatably driven by a motor which is controlled by the relay, whereby the direction of the received wave is so accurately determined that the instrument can he used for location of position by triangulation on radio sending stations.

Another object is to provide a relay which, though it may comprise part of the local audiofrequency electronic oscillator circuit, can operate efficiently therewith and furnish ample power with slight excitation and without appreciably detuning the circuit.

Other objects and advantages will become apparent from the following specification wherein reference is made to the drawing in which ig. l is a front elevation, partly in section, of preferred form of the relay and with a radio receiving set connected thereto;

Fig. 2 is a side elevation, partly in section, of the relay illustrated in Fig. 1; and

3 is a graph showing the current relatiom ships in the various coils of the relay.

Referring to Figs. 1 and 2, the preferret. form of relay shown therein for purposes of illustration comprises a base plate on which are mounted a pair of laminated field pieces 2 and 3, the field pieces being secured to the base in proper spaced relation therefrom by suitable bolts, as illustrated. The field pieces 2 and 3 are carried on the base with the pole faces of one spaced from the pole faces of the other so as to provide air gaps 3 and 5 between adjacent pole faces respectively, the air gap a being defined by the pole face 6 of the field piece 2 and the pole face I of the field piece 3, and the air gap a being defined by the pole face 3 of the field piece 2 and the pole face 9 of the field piece 3.

A laminated armature it is pivotally mounted on a pivot or bearing H which, in turn, may be secured in position by suitable plates or brackets i2 of brass or other non-magnetic material and which are connected to the field. pieces 2 and 3, or to the base, as desired. The axis of the pivot ii lies in a plane which is normal to the base i and extends midway between the pole faces 5 and i and also midway between the pole faces 8 and 9. The pivotal aXis itself is at right angles to the plane of the base and may be positioned along said normal plane either midway between the pole faces 8 and 9 or therebeyond in a. direction away from the pole faces 6 and 1 and toward the switches which are later described herein.

The armature it normally occupies a neutral position midway between the pole faces 5 and l and midway between the pole faces 8 and ii and is free to swing either direction. A counterweight portion iiis provided on the armature and is arranged at the opposite side of the axis of the pivot or bearing it from the other portion of the armature so as to position the center of gravity of the armature at the pivotal axis. Thi prevents swinging of the armature due to unbalanced inertia forces which would otherwise be caused by sudden lateral movements, jerking, or rocking of the airplane or vehicle.

The relay normally operates push buttons of self-restoring switches which, in turn, control the circuits of the steering mechanism of vehicles or other mechanism to be controlled. More broadly, it is arranged to open and close switches in the control circuits of anything to be controlled in response to movements of the relay, as for example, a reversible driving motor for the loop of a radio receiver used for triangulation.

In the form illustrated, two self-restoring snap action switches 25 are provided, thes switches being carried on the base i and being arranged on opposite sides of the counterweight portion M of the armature, lhe switche are preferably of the type shown and described in U. S. Patent No. 1,960,020, issued May 22, 1934, to P. K. McGall. Switches of this type are self-restoring and of extreme sensitivity, and snap from one contact position to another upon the application and withdrawal of very slight forces to the push buttons thereof, a more fully described in said Letters Patent.

The switches 65 have push buttons iii, respectively, one of which is positioned to be engaged and operated when the armature it is swung in one direction about its pivot it from neutral position, and the other of which is positioned to be engaged and operated by the armature when the armature it is swung in the opposite direction from neutral position. The forc applied to the push buttons by the armature in either instance is withdrawn when the armature operates the opposite push button and the push buttons are self-restoring to starting position. The push outtons also act as centering devices to urge the armature iii lightly into neutral position and mechanically maintain it in neutral position in a condition of somewhat unstable equilibrium.

armature is free to swing against the restraining force of the switches through a sufiicie'nt angle in both directions from its neutral position to dispose its outer end portion in contact with t pole faces (5 and '3, respectively, wh n th armature and field are excited.

It is often desirable that the switches be adjustable toward and away from the neutral position of rrnature and for this purpose they may be mounted on brackets ill on the base. Each of the switches is mounted on its associated bracket by a screw 58 which passes therethrough near one end thereof. The switch can be swung thr h a slight angle about the as scciated screw it by means of an accurate adjusting screw it. The screw is fits under tension in a threaded bore in the sidewall of the associated bracket, as illustrated in Figs, 1 and 2, and is connected to the switch so as to swing the switch in opposite directions to dispose the push button it at different adjusted positions relative to the neutral position of the armature.

Means are provided for polarizing the field pieces 2 and 3, and, in the form illustrated, this oeans comprises magnetizing coils 2i and 22 which surround the field pieces 2 and 3, respecively. The coils 2i and 22 may be connected in parallel or in series. In case a direct current is present, as in a vacuum tube push pull output, the coils t! and 22 may be divided in two and half of each placed on each leg of the pole piece, thereby eliminating any direct current magnetic field which would unbalance the pull on the armature. The field coils 2i and 22 themselves also may constitute the oscillator coils of the local oscillator circuit. Fixedly mounted with respect to the field pieces 2 and 3 and base i and in surrounding relation to the armature it is an armature coil 23.

As heretofore mentioned, the armature can swing through a sufiicient angle to contact the pole faces 5 and '5. Since the air gaps and 5 are or approximately the same width, however, and since the pivot or hearing ii is nearer to the space 5 than to the space 4, the armature cannot contact the pole faces 8 and 9 as it is restrained therefrom by engagement of its outermost end portion with the pole faces 6 and l.

The pole faces 6 and i are shaded by suitable short circuited coils 2d and 25, respectively. Since the armature contacts one or the other of these pole faces a and i when it is a maximum position from neutral, it forms with the pole pieces a low reluctance path from the inside of the shading coil to the outside thereof and return. Thus th armature it cooperates with the field pieces 2 and respectively, to render the shading coils and 25 effective for reducing the effects of harmonics which may be introduced into the circuit by the electronic oscillator and to avoid chattering when the main fiux is zero. It should be noted that when the armature is in contact with one of the pole facs 6 and l, the entire magnetic circuit of the particular pole piece is not shorted through the armature because of the space between the pole faces 3 and 9 and the armature. Furthermore, since the armature has moved a considerable distance away from the pole faces of one pole piece when it is in contact is not energized, but the slightest amount o rent in the armature coil works together with the pull of the pole faces to swing the a nature to right or left out of neutral position. The armature, due to the position of the pivot, and the absence of a centering is in unstable neutral equilibrium except for the slight push of the push buttons and thus, when it moves from new tral position and approaches the pole faces of one pole piece and recedes from the other, it operates with a snap action and ample power to operate the push buttons upon excitation by very slight armature currents.

To better illustrate the operaton oi the relay, its operation is described in connection w circuit with which it is combined for 1 V of airplanes and like and "-l is best illustrated in Fig. 1. In the steering of moving veno power th angle between the direction in which the plane or" the loop is pointed and the direction of initting station is equal to 99, the received signo.1 is zero, as no lines of flux cut the loop. rotating the loop connected to the receiver noting the point at which the signal disa; peas, the direction of the transinit i g sta can be :1 its switches to be used for this purpose since can he made responsive to the change in direction of the current received by the loop as the loop turns from one side or other of the zero signal point.

'adio receiving set 39 as disclosed States Letters Patent No. Cr. M. Earner on December 6,

loop antenna through the loop and ng circuit of the receiver is his local radio frequency oscillator Ci lUUJ. of which the relay device forrns a part. Whel... no signal is received, no output i the receiver is obtained. When the set is t lar station and the plane of slightly from 96 from the directicinitting station, t t a signal is received and second detector is modulated b frequency oscillator. This, n t" n, is am. and applied through the ter ture coil 23 of the relay. cilia-tor circuit energizes t .e through the terminals of 5.46

The current through the ture coils causes the armature [G to swing to the the right, depending upon the direc'lcn of of current through the loop 3| and the electrical connections between the output and the coil 2.3. Means are provided in the receiver to make the armature current approximately in phase or 139 out or" phase with the field current so as to cause magnetic deflection of the armature relative to the 1 1d pieces, when a signal is received.

The shaded poles 2d 25 prevent fluctuation or flutter of the armature when a strong signal distorts the output to the armature by introducing harmonics. These harmonics, particularly the harmonics due to overloading the thermionic tubes of the set, are very pronounced, particularly the second harmonic which may even cause the armature current resultant to be in the wrong direction if permitted to be effective as in the prior art. However. their effect is negligible in the present relay and circuit.

Assuming the circuit is used to steer an airplane automatically in flight toward the home station, when the airplane and consequently the axis of the loop antenna are pointed cl 'ectly toward the trans itting station point of destination, no s -al is race ed. these conditions, the a; nature is central or neutral position v n the air gas and consequently neit r of the switches is operated. If the plane turns out of alignin nt with the station, current is generated in tne 160p and thereby a current of uniform ph se is caus iiow through the field coils 25 ans ulatecl current, either irphase there. is caused to flow t coil 23. interrelation of the zna of the coils causes he Elllllflt. direction or the other, 1g upon ivhetl'ier the plane is heading to the right or left of its true course.

As the armature i9 approaches the pole face "i or l, as the case may be, its attractive force is very rapidly and its movement corespondingly increased so that it moves with a nap action when it leaves the neutral position. The lower extremity of the armature, or the counterweight M, contacts and pushes one of the push buttons it: of the snap action switches. snap action of the armature, combined with snap action of the particular switch, causes instantaneous electrical contact through the switches to control any external circuit connected thereto. The switches are operative to close and open the control circuits in a manner such that when the plane is heading to the right of its true course, the controls are operated to steer it that it heads to the left until it assumes true course, and vice versa. For purposes of illustration the operating for the controls is shown as a reversible electric motor it having its field circuit connected to the supply voltage and having its armature windconnected through the switches to the operating current as illustrated so that the armature circuit can be reversed relative to the field circuit. The extreme position reached by the armature use to an oil-course travel continues until t ..e plane is again on its course, whereupon the armature moves to its neutral position. If the plane heads off its course in the a, Josite direction, the current in the coil 23 reses relative to its previous direction and the ature rnoves to repeat the operations in the opposite direction. fhus, the phase of the armature current, and consequently, the magnetic of the armature is reversed relative to the field current, depending upon the course of the plane, but the phase of the field remains uniform.

In prior structures, since the armature is magnetically centered, the centering flux must be overcome and a relatively high armature current is required to swing the armature. To reduce the current required in prior structures, the armature thereof is positioned to operate out of the main field and only in the stray field. Even if the armature normally operating in the stray field were to contact the pole pieces, too high an armature current would be required to restore it to neutral.

In the present relay, the major flux field is used instead of the stray field and the armature operates directly in the major flux field, magnetic centering is eliminated, and unstable equilibrium of the armature in neutral position is provided because of the magnetic pull of the field pieces. Therefore, a slight armature cur rent is sufficient for operation.

Thus, in prior structures, a magnetically centered armature having a neutral position of relatively stable equilibrium which must be overcome by the armature current is provided, whereas in the present relay a mechanically centered armature having a neutral position of relatively unstable equilibrium which can readily be overcome by the armature current, is provided.

The change in the directions of the currents is illustrated in Fig. 3 wherein the curve A represents the current in the field coils 2! and 22. If the plane is heading to the left off its course, the current in the coil 23 would be such as indicated by the curve B, and when the plane is heading to the right off its course, the current in the coil 23 is such as illustrated by the curve C. Consequently, the force on the armature If) is reversed as the plane heads to the right or left of its course, and the armature therefore moved to the opposite pole piece.

As hereinbefore mentioned, the output from electronic oscillators is non-sinusoidal. Nonsinusoidal waves may be plotted as a sine wave with a plurality of harmonic waves of sinusoidal shape but of higher frequency than the fundamental. By virtue of the shading coils 24 and 25, the efiect of the harmonics which otherwise would distort the wave are nullified, and only the fundamental is effective to cause operation of the relay. This damping effect is very pronounced due to the low reluctance path provided by contact of the armature with the pole face 6 or ii within and adjacent the shading coils. Likewise, the metal path for magnetic flux is not closed at the pole faces 3 and 9 and consequently the reluctance is not so greatly reduced by contact of the armature and pole pieces as to detune the oscillator circuit of which the field coils, pole pieces and armature form a part.

Having thus described my invention, I claim:

1. An alternating current relay including a of oppositely positioned and separate generally iJ-shaped pole pieces, each pole piece having a pair of spaced pole faces arranged in spaced relation to the pole faces of the other pole piece so as to define two spaced air gaps each gap being a major nux path between its defining pole faces, an armature extending into and movable in'both of said air gaps and operable by the major fiux in both of said gaps when said pole pieces are polarized, means pivotally supporting the armature for oscillation about a pivotal axis which lies in a plane extending through the centers of said air gaps, said pivotal axis being positioned along said plane nearer to one of said air gaps than to the other so that the armature can swing into contact with the pole faces defining the one of the air gaps which is farther from the pivotal axis without swinging into contact with the pole faces defining the other of the said gaps which is nearer the pivotal axis, means o'perable by the armature, upon swinging of the armature to different positions, to effect control of a mechanism, field coil means for the pole pieces, respectively, and operative when excited by alternating current to create major flux paths across said gaps, and an armature coil operative when excited by alternating current in a predetermined phase relationship to the excitation of the field coil means to move the armature into contact with the pole faces which are farther from the pivotal axis, and means yieldably opposing movement of the armature from a neutral position out of contact with all of said pole faces.

2. An alternating current relay comprising separate pole means having two pairs of spaced pole faces, the pole faces of each pair defining separate air gaps with the pole faces of the other pair, respectively, and each gap being a major flux path between the pole pieces, an armature extending into both of said air gaps, means supporting said armature for oscillation in both air gaps in opposite directions a distance sufficient to permit said armature to contact the pole faces defining one gap, respectively, means to constrain the armature from contact with the pole faces defining the other gap, switch means normally yieldably holding the armature in a neutral position wherein the armature is out of contact with all of the pole faces and opposing movement of the aramture out of said neutral position, the opposing force of said switch means being decrescent as the armature moves out of neutral position and approaches one of the pole faces, whereby excitation of the armature sufficiently to cause the armature to move out from neutral position assures movement of the armature to an extreme position in contact with a pole face without an increase in excitation, field coil means for the pole means and operative when excited by alternating current to create major flux across both of said gaps, an armature coil operative when excited by alternating current in a predetermined phase relationship to the excitation of the field coil means to move the armature out of said neutral position and into contact with the pole faces, respectively, of one of said air gaps.

3. A high sensitivity alternating current polarized relay comprising magnetic field means having two pairs of pole faces, the pole faces of each pair being adjacent to but spaced from each other, whereby each pair of pole faces defines an air gap, an armature extending into both of said air gaps, means supporting the armature for oscillation from a neutral position with respect to said pole faces to extreme positions wherein it contacts with the pole faces, respectively, of one of said pairs of faces, said armature when in contact with said one pole face of said one pair of pole faces being displaced by an air gap from both of the pole faces of the other pair of pole faces so as to leave an air gap in the magnetic circuit which includes the armature and said one pole face, a pair of snap action, self-restoring switches connected to a control circuit for operation thereof, the selfrestoring part of said switches being arranged at opposite sides of said armature and engageable therewith when the armature is in neutral position and cooperating with the armature for yieldably constraining the armature to said neutral position when the armature is unexcited.

4. A high sensitivity alternating current relay comprising a pair of pole pieces, each pole piece having a pair of pole faces, field coils for the pole pieces, respectively, each pole face of one pole piece forming an air gap with a different pole face of the other pole piece, said air gaps each being a major flux path of the pole pieces when the coils are excited, an armature extending into at least one of said air gaps, means spaced from both air gaps and supporting the armature for movement from a neutral position in said one of the air gaps to positions wherein it is in contact with one of the pole faces defining said one air gap and constraining the armature'from contact with the pole pieces except at said last mentioned pole face, so as to leave, at all times, an air gap in the magnetic circuit which includes the armature and pole face with which the armature is in contact, an exciting coil for the armature, means yieldably urging the armature to said neutral position with a force which increases as the armature approaches neutral position and decreases as the armature recedes from neutral position, means rendered operative for controlling a mechanism when the armature moves a predetermined distance from said neutral position.

5. A highly sensitive polarized alternating current relay comprising an oscillatable armature, snap action self-restoring switch means operatively associated with the armature and normally opposing movement of said armature from a neutral position and operable to reduce the opposing force on the armature suddenly upon slight movement of the armature from said neutral position, means operable by the armature when the armature moves out of said neutral position to operate said switches, and electromagnetic means operatively associated with the armature for causing said armature to be moved magnetically from said neutral position and with increasingly effective magnetic force as the armature recedes from neutral position when the electromagnetic means is energized by alternating current.

6. A highly sensitive polarized alternating current relay comprising an oscillatable armature, means normally yieldably holding said armature in a neutral position and opposing movement of the armature from said neutral position and operable to reduce the opposing force on the armature suddenly upon slight movement from neutral position, electromagnetic means operatively associated with the armature and having a pole face engageable by the armature and operative, in cooperation with said means, for causing the armature to move from said neutral position with a snap action against said pole face when the electromagnetic means is energized by alternating current, said armature and said electromagnetic means being operatively associated in a manner such that the reluctance of the electromagnetic means remains substantially constant at all times during its energization and in all positions of the armature.

7. An alternating current relay comprising pole means having a pair of pole faces defining an air gap, an armature extending into said air gap, a bearing supporting the armature for oscillation in opposite directions from a neutral position between the pole faces a distance sufi'icient to permit said armature to contact the pole faces respectively, said armature having its center of gravity substantially at the axis of the bearing, exciting means for the pole faces and armature respectively, and operative when the exciting means are concurrently excited by alternating current in a predetermined phase relationship to move the armature to the pole faces, respectively, means operative to return the armature to a neutral position out of contact with the pole faces and yieldably to hold the armature in said neutral position when the armature is unexcited, and operative to oppose movement of the armature out of neutral position with an opposing force which decreases rapidly after the armature is moved out of neutral position, and means operated by movement of the armature to predetermined positions to control a mechanism.

8. A high sensitivity alternating current relay comprising pole means having a pair of spaced pole faces, field coil means for the pole means and operative when excited by alternating current to create a major flux between said faces, an armature having a portion extending into the major flux path between said spaced faces of the pole means, an armature coil operative when excited by alternating current in a predetermined phase relationship to the excitation of the field coil means to move the armature into contact with the pole faces, respectively, switch means for yieldably holding the armature mechanically in a neutral position between said spaced faces when the armature is unexcited, said switch means being operable to reduce the opposing force on the armature suddenly upon a slight movement of the armature from said neutral position, and means for preventing short circuiting of the armature flux through the pole means of the armature when the armature is in contact with either of said pole faces.

9. A high sensitivity alternating current polarized relay comprising magnetic field means having two pairs of pole faces, the pole faces of each pair being adjacent to but spaced from each other to form two separate air gaps each of which is a major flux path of the pole means when the pole means are excited, an armature extending into at least one of said air gaps, means supporting the armature for oscillation from a neutral position between said pole faces to extreme positions wherein it contacts the pole faces, respectively, of one of said pairs of pole faces, and is constrained from contact with the pole faces of the other pair so as to leave, at all times, an air gap in the magnetic circuit which includes the armature and the pole face with which the armature is in contact, snap action, self-restoring switch means connected to a control circuit for operation thereof, the self-restoring part of said switch means being operatively connected to the armature and yieldably opposing movement of the armature from said neutral position, coil means for the armature and for the magnetic field means, respectively, and operative when excited, respectively, by alternating current in predetermined phase relations to each other to move the armature from said neutral position.

KNUD J. KNUDSEN. 

